The Tandy Radioshack TRS-80 Model I is a desktop computer launched in 1977 by Tandy and sold through their Radio Shack stores. It is one of the earliest mass-marketed retail computers of the time.

THe computer runs on a Zilog Z80 CPU, has 4Kbyte of memory and floating point Level 1 Basic interpreter in ROM. The video output is 64x16 characters monochrome. Memory could be expanded up to 48 KByte and up to four floppy disk drives and/or hard drives could be added.

As was common with a lot of computers of the time, the monitor had a visible flicker when the CPU would access the screen memory. Programmers worked around this issue and many arcade-style games are available for the TRS-80 platform.

The model I has no built in speaker but square wave tones can be produced by outputting data to the cassette port and plugging an amplifier into the cassette "Mic" line. A lot of games used this ability for sound effects. Atari joysticks could be used on the TRS-80 using an adapter.

The year 1977 was a defining year for the home computer market. The three main computer systems that were introduced that year are now considered part of the 1977 Trinity of computing:

• Commodore PET 2001
• Tandy Radioshack TRS-80 Model 1
• Apple II

The Z80 quickly became popular in the personal computer market, with many early personal computers, such as the TRS-80 and Sinclair ZX80, using the Z80 as their central processing unit (CPU). It was also widely used in home computers, such as the MSX range, SORD, and the Amstrad CPC, as well as in many arcade games. Additionally, it was also used in other applications such as industrial control systems, and embedded systems. The Z80 was widely used until the mid-1980s, when it was gradually replaced by newer microprocessors such as the Intel 80286 and the Motorola 68000.

The Z80 microprocessor was developed by Zilog, a company founded by Federico Faggin in 1974. The Z80 was released in July 1976, as a successor to the Intel 8080. It was designed to be fully compatible with the 8080, but also included new features such as an improved instruction set, more powerful interrupts, and a more sophisticated memory management system.

Originally the Z80 was intended for use in embedded systems, just as the 8080 CPU. But the combination of compatibility, superior performance to other CPUs of the era, and the affordability led to a widespread use in arcade video game systems, and later in home computers such as the Osborne 1, TRS-80, ColecoVision, ZX Spectrum, MSX, Sega's Master System and many more. The Z-80 ran the original Pac-Man arcade cabinet. The Z-80 was used even in the Game Gear (1990s), and the TI-81 and succeeding graphic calculators.

The Z-80 remained in production until June of 2024, 48 years after its original release. Zilog replaced the processor with its successor the eZ80, an 8-bit microprocessor that features expanded memory addressing up to 16 megabytes, and running up to 50MHz, comparable to a Z80 clocked at 150MHz.